In typical control valves, a trim assembly, such as a valve cage or valve cage and cage retainer, may provide guidance for a valve plug as the valve plug moves from a closed position in which the valve plug sealingly engages a valve seat to an open position in which the valve plug is disposed away from the valve seat. When the control valve is in the open position, fluid flows from an inlet, passes through a passage between the valve seat and the valve plug, passes through the trim assembly, and exits through an outlet. In addition to guiding the valve plug, a trim assembly can also be used for additional functions, such as noise attenuation.
The principles typically used to attenuate noise in a control valve using a trim assembly are: reduced jet size, staged pressure reduction, optimal low high and low pressure recovery, jet independence, and peak frequency shifting. However, due to manufacturing limitations, implementation of as many of these principles as possible was performed linearly, in series, and was primarily limited to radially plane geometry and required large outer diameter trim assemblies and wide trim assembly cross sections.
Referring to FIG. 1, a typical control valve 10 is shown. Control valve 10 generally includes a valve body 12 having an inlet 14, an outlet 16, and a passageway 18 disposed between inlet 14 and outlet 16. A valve seat 24 is disposed in passageway 18 between inlet 14 and outlet 16 and a solid trim assembly 22 is disposed within valve body 12. A fluid control member, such as valve plug 26, is positioned within valve body 12 and is disposed within trim assembly 22. Valve plug 26 interacts with the valve seat 24 to control or modulate fluid flow through the valve body 12 of control valve 10, such that valve plug 26 sealingly engages valve seat 24 in a closed position and is spaced away from valve seat 24 in an open position. A stem 28 is connected to valve plug 26 at one end and to an actuator 30 at another end. Actuator 30 controls movement of valve plug 26 within trim assembly 22. Trim assembly 22 is positioned adjacent valve seat 24 and proximate valve plug 26 to provide guidance for valve plug 26.
In traditional applications, trim assembly 22 has a plurality of radially extending passages 20 formed through a circumferential wall of trim assembly 22, which are used to attenuate the noise produced as the fluid passes through trim assembly 22. Passages 20 are spaced specifically such that the jets of fluid that are produced as the fluid exits passages 20 do not converge and produce aerodynamic noise. Trim assemblies 22 used in these types of fluid applications are typically used in a “flow up” orientation (e.g., the fluid enters the center of trim assembly 22 and passes from an inner surface to an outer surface of trim assembly 22) and the spacing of passages 20 that is crucial to reduce the aerodynamic noise is on the outer surface of trim assembly 22. The spacing of passages 20 on the inner surface of trim assembly 22 can also be important, as this spacing is used to keep sufficient space between passages 20 to not allow flow to pass through more passages 20 than desired for accurate flow characteristics throughout the travel of valve plug 26.
For solid trim assemblies 22 used in fluid applications where the process conditions produce aerodynamic noise as the fluid flows through control valve 11, drilled holes through the circumferential wall of trim assembly 22 are typically used to form passages 20. However, implementation of multiple noise attenuation principles, such as reduced jet size, staged pressure reduction, optimal low high and low pressure recovery, jet independence, and peak frequency shifting, is severely limited due to limitations of this manufacturing technique.